Blood filters are used in a number of medical environments to remove unwanted particulates from a blood stream. For example, an arterial blood filter is commonly used in an extracorporeal circuit for cardiopulmonary bypass surgery to help minimize the dangers of embolism formation. Ordinarily, an arterial blood filter employed in conjunction with an oxygenator system is placed between the oxygenator and patient. Blood is directed from the oxygenator to the filter via a blood pump, and the oxygenated blood is filtered to remove emboli, bubbles, or other particles (generally "particles") before being returned to the patient.
Blood filters used in extracorporeal circuits should have a small priming volume to reduce the trauma to the patient from temporary loss of blood. In addition, extracorporeal filters should be effective in removing all the foreign particles in the blood without an excessive pressure drop, which creates a need for more pump work. Importantly, there should be no, or at least a minimal, chance of blockage, and filter performance should not decrease during the expected useful life of the filter, even during worst case partial plugging of the filter system. Finally, blood filters are disposable and thus should be relatively inexpensive since the filter has to be replaced after every procedure.
In conventional blood filters, a passive element such as a sock-like tubular cartridge, is installed in a generally cylindrical filter housing. Blood enters the housing on an inlet side (inside or outside) of the cartridge and passes through the cartridge walls to the other, outlet side. Because of the large surface area needed to filter an adequate flow of blood, conventional blood filters typically require a priming volume of 200 cc or more, which is proportionally significant in the overall extracorporeal circuit priming volume. Furthermore, fine mesh filter cartridges along with the housings are relatively expensive to continually replace.
Bubble formation may be a problem from the oxygenation process and simple air traps are often used to capture the bubbles before re-entering the patient. Other devices known utilize sensors to detect bubbles in the extracorporeal tubing downstream from the oxygenator. Such sensor devices, however, simply shut off blood flow altogether, or re-rout blood containing bubbles back through a pumping system. See, for example, U.S. Pat. Nos. 4,280,495 and 5,188,604. These setups may detect bubbles, but they also completely disrupt the return blood flow to the patient, which is counterproductive.
In short, there is a need for an effective, inexpensive blood filter with a low priming volume.